Audio reactor



Patented Nov. 26, 1946 AUDIO REAUI'QR Morris Sander, Philadelphia,

Pa, asslgnor to Radio Corporation of America, a. corporation of Delaware Application September 20, 1943, Serial No. 503,054

7 Claims. 1

My present invention relates to a reactor for use at audio frequencies, the inductance of which it is desired to vary over a predetermined range. In practice it has been found difficult to obtain adequate inductance change in high Q, low-frequency inductors. In one application of the present invention, operating at about 939 cycles per second, I have been able to obtain an inductance variation of ;Ll5%, the Q of the coil being between 30 and 35.

In accordance with the invention, the reactor is made adjustable and comprises a coil form oi insulating material having a central and two end compartments which are open-ended, in alignment and disposed in parallel relation. A coil of wire is wound around the coil form in a direction transverse to the direction of the compartments, and a fixed laminated iron core having an air gap is positioned within each of the end compartments. There is further provided within the central compartment a powdered-iron core which is capable of adjustment relative to the coil and air-gaps of the fixed cores for the purpose of varying the inductance of the reactor.

The novel features characteristic or" my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its construction and mode of operation together with the objects and advantages thereof, will best be understood by reference to the following description taken in connection with theaccompanying drawing in which Fig. 1 is a plan view to scale of the reactor as- 'serncly in accordance with the invention;

Fig. 2 is a front elevational view of Fig. 1; Fig. 3 is a view in cross-section taken along the line 3-3 in Fig. 1, showing the two-part fixed laminated core;

Fig. i is a cross-section taken along the line l-d in Fig. 1;

Fig. 5 shows the complete assembly of the reactor enclosed in a casing; Fig. 6 is a detail view means, and

7 represents the schematic circuit of the reactor.

Referring to Fig. l the reacto comprises an inductance winding or coil 5 which is wound, in a plane parallel to the surface of the drawing, around a centrally located spool or coil form 2. The coil leads are indicated at 3 and t. The spool '2 may be of moulded nylon or other suitable insulating material and is provided with a central compartment 5, square-shaped in crosssection, and two similar end compartments 6 and of the core adjusting (Cla I'll-242).

three compartments are open-ended at the top and bottom, are aligned with one another, and disposed in parallel relation. The central com partnoent which is extended somewhat above and below the two end compartments, as shown more clearly in Fig. 4, is adapted to receive an iron core made of compressed iron dust, the core being sliclably adjustable within the compartment 5 by means to be hereinafter described.

The two end compartments" 6, l are each adapted to receive the center leg 9, Si of a composite fixed core M3 constituted by stacks of laminations which may be of Numetal (a niclzel alloy) or othe suitable material. For convenience of assembly the fixed laminated core it is made of two similar parts it and it which are paired, as shown more clearly in Fig. 3, to provide the center leg d, 9', the portions of which are adapted to be inserted into an end compartment from opposite sides and to be positioned in fitted spaced relation to provide an air gap iii between them.

In order to maintain the pair of laminated cores ill in fixed parallel relation and also to rigidly retain in position the two parts M, ii of each. core there is provided at each end a clamp ing plate 92 to which a pair of brackets l3 are spot welded or otherwise attached. The two brackets of each clamping plate are properly spaced and are adapted to embrace the corresponding sides of the two fixed cores it, and by means of four screws it the oppositely disposed clamping plates it are held together. Each plate is provided with a flange or foot portion i5 for convenience or" attachment by means of screws, rivets or otherwise to a base plate it (Fig. 5).

The base plate to has attached to it a pair of terminals ll, ll to which the leads 3, d from the inductance coil l are connected. A suitable rectangular-shaped metal can housing to is fitted over the entire assembly and is soldered or otherwise connected to an upturned flange it of the base plate it. The can housing is provided at its two shorter sides with a pair of flanges or foot portions ill for attachment to a chassis or other mounting, and is further provided in its upper wall with an opening through which there is passed a screw shaft 26 ably adjust the iron core 8 within the center compartment 5 of the coil form 2.

The iron dust core 8 is also square-like in crosssection and is provided with a centrally located bore 22 which extends fo about three-quarters of the length of the core from the bottom. The remaining portion of the core above the bore is which is adapted to sliding,

internally threaded and is adapted to ride on the screw shaft. Frictionally within the bore and positioned near the lower end thereof is a nut plate Or retaining member 23 through which the screw shaft is also threaded. A compression spring 25 is concentrically arranged around the shaft within the bore and extends between the nut plate and the opposing internal rim portion of the core in order to take up any play or back lash between the core and the screw shaft.

In order that the adjustable core may be accurately centered within its compartment there is utilized a block member or plug 25 formed with an aperture 28 within which the lower end of the screw shaft is adapted to be seated. The centering block is suitably attached by screws, rivets, or the like, to the cover plate i8, is simi- While I have shown and described a preferred embodiment of my invention, it will be underlarly shaped in cross-section as the center comsufiicient length to extend end and to partment, and is of into said compartment at the lower be snugly fitted therein.

In order that the. core may be adjustably set from the outside of the can housing, the latter is provided in its top'wall with an aperture it through which there extends an externally threaded bushing 21!, the intermediate portion of which is provided with a first disc member 36 and a second larger disc member 30. The two disc members may form an integral part of the bushor otherwise mounted thereon, as by means of a forced fit. The larger disc 3% is concentrically arranged with respect to the housing aperture it and is soldered to 29, the bushing and its associated parts are clamped in position. The bushing is adapted to receive within its bore the upper unthreaded end of the screw shaft 25 which is retained therein and confined only to rotary motion by means of a C washer 3i engaging a circumferential groove 32 in the shaft. A washer 33 and a spring washer 3d are interposed between the C washer and the bushing in order to lock the shaft against vertical movement. For effecting the desired adjustment of the core, rotation of the screw shaft by means of a suitable tool, such as a screw driver, will cause the core to ride up or down depending upon the direction of shaft rotation. An internally tapped cap 35 may be provided to fit over the exposed end of the bushing on which the screw head is seated to prevent tampering after an adjustment has been made.

In one embodiment of the invention the coil consisted of 1,000. turns of wire, the air gap in each fixed core was 1", and the adjustable core was 1" in length and .594" square. With the adjustable core 8 all the way in (Fig. 5) and a source of voltage at the input terminals of the reactor of 1 volt and a frequency of 1,000 cycles, the inductance was approximately 0.47 henry, whereas with the core all the way out, the inductance was approximately.0.36 henry, an inductance change of approximately 30%,' or 115% from a mean core adjustment giving 0.415 henry. The inductance change is due to the fact that the powdered iron dust core varies the inductance not only by acting on the turns of the coil but also by short circuiting the air gapso'f the fixed core stacks.

In contradistinction to the usual reactor assemblies employed in radio apparatus, the inductance and the Q of the reactor of the present invention are not affected by the can housing for the reason that. the fixed laminated cores act the top wall of the housing. By means of a washer 28 and a locknut stood that various modifications and changes will occur to those skilled in the art without depart ing from the spirit and scope of this invention. I therefore contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim is:

1..A reactor comprising a coil form of insulating material having a, central and two end compartments, said compartments being open-ended, in alignment and disposed in parallel relation, a coil of wire wound around the coil form in a direction transverse to the direction of the compartments, a fixed laminated iron core extending into each of the end compartments, and an adjustable powdered-iron core extending into the central,

compartment.

2. A variable reactor for audio frequencies com= prising a coil form of insulating material having a central and two end compartments which are disposed in parallel relation, a coil wound around the coil form in a direction transverse to the direction of the compartments, a fixed iron core extending into each of the end compartments, said fixed cores each having an air gap located in the field of the coil, and a powdered-iron core adjustably movable within the central compartment for varying the inductance of the reactor.

3. A variable reactor for audio frequencies comprising a coil form of insulating material having a central and two end compartments, said compartments being open-ended, in alignment and disposed in parallel relation, a coil of wire wound around the coil form in a direction transverse to the direction of the compartments, a fixed laminated iron core provided with an air gap extending into each of the end compartments, and an adjustable powdered-iron core movable within the central compartment capable of varying the inductance of the reactor.

4. A variable reactor in accordance with the invention defined in claim 3 wherein the reactor is housed within a container provided with an aperture which is aligned with the central compartment and through which there is adapted to 59 extend the means for adjusting the powderediron core.

5. A reactor comprising a coil form of insulating material having a central and two end compartments said compartments being open-ended,

in alignment and disposed in parallel relation, a

60 tending into coil of wire wound around the coil form in a direction transverse to the direction of the compartments, a pair of three-limbed laminated iron cores having their respective central limbs exone of the end-compartments and their outer limbs positioned externally of the coil, and an adjustable powdered-iron core extending into the central compartment.

6. A variable reactor for audio frequencies comprising a coil form of insulating material having a central and two end compartments which are disposed in parallel relation, a coil wound around the coil form in a direction transverse to the direction of the.compartments, a pair of threelimbed iron cores having their respective central limbs extending into one of the end compartments and their outer limbs positioned externally of the coil, each of said cores constituting a closed magnetic circuit except for an air gap in the central limb located in the field of the coil,

and a powdered-iron core adjustably movable within the central compartment relatively to the coil and air gaps for varying the inductance of the reactor.

7. A variable reactor for audio frequencies comprising a coil form of insulating material having a central and two end compartments, said cornpartments being open-ended, in alignment and disposed in parallel relation, a. coil of wire wound around the coil form in a direction transverse to 10 

